Spark plug



l.. A. HYLAND SPARK PLUG `lune 27, 1944.

I5 Sheets-Shee't l Filed om. 9, 1928 Lan/rence /l/l/ymd L. A. HYLAND SPARK PLUG Filed Oct. 9` 1928 3 Sheets-Sheet 2 gjm/UWM ah/rence ffy/@72d June 27, 1944.

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June.27, 1944. A. HYLAND SPARK PLUG Filed Oct. 9, 1928 3 Sheets--Shee'fl 5 Syvum/WO@ Lan/rence @Zand 3% Wawi Patented June 27, 1944 I SPARK PLUG Lawrence A. Hyland, Washington, D. C., assignor,

by mesne assignments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application October 9, 1928, Serial N0. 311,354

39 Claims.

My invention relates broadly to spark plugs and more particularly to a construction of electrically shielded spark plug. l

One of the objects of my invention is to provide a construction of spark plug having means for electrically shielding the plug and ignition circuit which is connected thereto for eliminating interference between the ignition system and the adjacent electron tube amplification apparatus or telephone circuits.

Another object of my invention is to provide a construction of spark plug, which is equipped with high potential insulation for insuring the spark plug against electrical break down, with means for enclosing the plug within an electrical shield which forms an electrical continuation of the shield for the ignition wire which enters the plug.

Still another object of my invention is to provide a construction of electrically shielded spark plug in which a tubular shaped insulation member provides a sleeve or shell-like separator between the high potential electrode of the Spark plug and an exterior shielding casing for assembly of the plug inexpensively on a quantity production basis.

Other and further objects of my invention reside in a construction of spark plug in which mica insulation may be employed to protect the spark plug against break down and separate the interior parts of the spark plug from an electrical shield which substantially encloses the parts of the plug and forms a bond with a flexible shield disposed about the ignition wire which enters the spark plug.

Other and further objects of my invention reside in the construction of spark plug described in the specification hereinafter following by reference to the accompanying drawings in which:

i Figure 1 is a longitudinal cross-sectional view "taken through the spark plug construction of my invention; Fig. 2 is a cross-sectional view through the spark plug construction of Fig. l on line 2 2 thereof; Fig. 3 is a cross-sectional view taken through the spark plug of Fig. 1 on line 3-3 thereof; Fig. 4 is a cross-sectional view through the spark kplug on line 4--4 of Fig. l; Fig. 5 is a longitudinal cross-sectional view through a spark plug of modified construction showing the application of my invention thereto; Fig. 6 is a cross-sectional view through the spark plug on line 6 6 of Fig. 5; Fig. '7 is a crosssectional view through the spark plug on line l-l of Fig. 5; Fig. 8 is across-sectional View through the spark plug taken on line 8-8 of Fig. 5; and Fig. 9k shows an application of the principles of my invention to a spark plug of modified construction where means are provided for radiating heat from the spark plug.

The spark plug of my invention is particularly adapted for aircraft engines. The spark discharges in the ignition system of an internal cornbustion engine on aircraftproduce highly undesirable interference with the operation of a radio receiving apparatus aboard aircraft. The periodic spark discharges of the ignition system of the aircraft engine set up electrical surges in the ignition wiring, which results in electromagnetic radiations which4 interfere with the reception of signals in the receiving system. The interference from the spark discharges of the engine does not occur upon any particular frequency but persists on all frequencies producing a disagreeable succession of noises in the receiving telephones which makes signal reception extremely unsatisfactory and at times impossible.

Radio communication on aircraft is extremely important, and in order to insure satisfactory communication, I have investigated various methods of avoiding interference between the ignition System of the internal combustion engine and the radio receiving circuits. I have found the construction of spark plug set forth herein to be highly successful in eliminating interference in the radio receiving system due to internal combustion engine operation.

The spark plug structure of my invention comprises a metallic casing employing a tubular member of mica for insulating the parts of the spark plug within the casing. The central electrode is rigidly secured within the casing and is insulated from the casing in a manner to withstand high potentials. The ignition wire which is electrostatically shielded enters the top of the casing and the shielding of the wire is electrically bonded to the casing. The ignition wire extends downwardly into the tubular insulating membery establishing connection with the central terminal of the spark plug.

I have illustrated the spark plug structure of my invention as particularly adapted for aircraft operation but it will be understood that such spark plugs may be used in other internal combustion engines where operation must be carried on in close proximity to radio receiving apparatus.

I have illustrated a number of modifications of l the spark plug structure oi my invention which will be understood by detailed reference to the drawings.

In Figure 1 I have shown the metallic casing or shell of the spark plug as having a screw threaded portion I for engaging a threaded aper `ture in the engine cylinder wall. The core of said plug has a central electrode or terminal 3 in the form of a stem or spindle which is insulated from the body by means of the mica tubular member or insulator 2 which fits around the central terminal 3. The metallic wedge-shaped centering members 4 and 5 serve with the tapered bore of portion to position and x the central terminal 3 within a metallic casing B which is in the form of a thin barrel or outer shell extending from said portion 25. Said portion 25 with said members 4 and 5 thus constitutes a support, in the form oi a cap or jacket, for the terminal 3, shielding 6 and interposed insulation. The gripping faces 24 connected integrally with the casing E enable the casing to be screw threaded into the first named metallic casing, with external screw threads on the portion 25 of the casing 6 engaging the internal screw threads on the portion 2G of said first named casing.

A gasket member is provided in the position shown for establishing a hermetic or gas-tight shield between the parts of the spark plug. Insulation member 29 just above the head serves to further insulate the central terminal from the side walls of the casing. I provide a cylindrical laminated tube or hollow insulating sleeve of mica represented at 'I enclosed in a mica sheath 2,. Tube I is recessed to provide a socket as shown at 36 and into this recess the head or plug terminal connection 9 of the central terminal 3 projects. The dielectric or mica member I closely embraces the terminal 3 and extends upward the full height o! the casing 6 in contact therewith as a lining for the same. The ignition wire 22 of the high tension conductor or cable connects electrically by a tip piece as represented at I0 to the spring connector 8 which constitutes a cable terminal connection that engages the ball or outlet 9 on the center electrode 3 to provide a quickly attachable and detachable connection. The distance from point I0 to the nearest point in free air without protective insulation other than free air is not less than three quarters of an inch or whatever limiting dimension will allow safe operation. It will be understood that special problems arise in ignition systems for aircraft engines not present in ground automotive ignition systems, for the reason that aircraft ignition systems are subjected to rareed atmospheres changing "the dielectric strengths of the air in proximity to the plugs. Hence any high potential point in the ignition system not cornpletely enclosed in a solid insulator must have a flash over distance to the nearest ground of at least 3A of an inch if the ignition system is to function at high altitudes. The ignition wire 22 is covered with insulation represented at 2i, and the insulation is in turn covered by a flexible electrical shield or sheath represented at I3, the shield extending through the apertured, recessed screw threaded cap or coupling nut I4 and terminating at metallic ring member I2. A gasket member, such as a copper asbestos washer I5, may be placed between the ring member I2 and the inner wall o! the screw threaded cap I4 so that when the screw threaded cap I4 is screwed to a position in which its interior threads at 23 engage the exterior threads on the end of the casing 6, an electrical bond will be established between the ignition wire or cable shielding at I3 and the plug shielding or sheath formed by the metallic casing 6 which is grounded through the threaded connection at I. The ignition wire extends to a position interior of the socket 35 in the mica insulation 1 and is provided with an insulated end cap 23 in the form of an enclosing sleeve or bushing which serves to center the ignition wire within the socket 35, permitting connection to be established between the spring cap 8 and the terminal 9. The central conductor 3 terminates in an electrode at 21 which is positioned adjacent the stationary electrode 28 for establishing the spark gap. The mica tubular member I provides a substantial body of insulation between the interior walls of the casing i and the ignition wire and central terminal.

In Fig. 5 I have shown a modified arrangement of establishing connection between the igni tion wire and central terminal where my invention is applied to a spark plug of different construction. The metallic casing 6 of the spark plug has the rolled mica tubular member 2 extending as a lining substantially throughout the length of the plug, the mica lining embracing the central electrode 3 for approximately half the height of the casing and embracing the insulation on the ignition wire along the remainder of the casing. The central terminal 3 is provided with a tip 32 to which ignition wire 22 is secured. The end of casing B terminates in an annular closure 30 extending over the upper edge of member 2 and against which the metallic washer I2 abuts, the washer I2 being secured to the electrostatic shield I3 and being maintained in place by means of screw threaded cap I4.

In Fig. 9 I have shown my invention applied to a type of spark plug having cooling ns 3| integrally connected to the casing 6 on the spark plug. The electrostatic shield I3 is bonded to the casing Ii by means similar to that described as to Fig. 5. It will be observed that the mica tubular member 2 extends substantially the en tire height of the plug providing the required insulation against high potential break down.

The spark plug of my invention has been found to be extremely practical in manufacture and production and successful in operation, and while I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

l. A spark plug comprising a metallic casing, a central terminal disposed in said casing, a tubular member of insulating material within said casing, said tubular member surrounding and supporting said central terminal, means for cen tering said terminal relatively to said casing comprising a plurality of metallic wedging members,

' one of which abuts the lower end of said tubular member, and a second insulating member surrounding the portion of said central terminal adjacent said wedging members, said casing being shaped to insure maintenance of said wedglng members in properly spaced relation to said insulating members and in proper relation to each other.

2. A spark plug comprising an outer metallic casing, a central terminal disposed in said casing, a tubular member of insulating material surrounding :and supporting said central terminal within the casing, means for centering said terminal relative to the casing. comprising a pair of wedging members surroundingsaid terminal, one of saidmernbers. abutting the lowerend .of said tubular member, the otherof-said members having wedging engagement'with said rst-named member, an insulating'membersurrounding the portion of said `central terminal adjacent said second-named wedging member, and means formed on said casing for wedging engagement kwith said rst-named wedging member,

3. A sparkplug comprising a bodystructure composed 'of solidly packedseries of laminae of insulating material, the said laminae being divided into two groups, eachcentrally apertured todiierent degrees, an ignition terminalsextending through thelower group of laminae, an ignition wire projected into theupper group of laminae for establishing connection Witlrsaid ignition terminal, a vmetallic casingl enclosingsaid body structure, a metallic sheath surrounding said ignition wire, and `means for connecting the metallic casing enclosing saidbody structure with the metallic sheath.

4. A spark plug comprising. a central electrode,v

an outer metallic casinghaving horizontally, vertically, and obliquely Adisposed inner-surfaces, a tubular member of insulating material engaging said horizontallyv disposed surface at its uppen end, and terminating substantially at the junction of said verticallyand obliquely disposed surfaces, a second insulating member below said flrst'named insulatingmember, a pair of wedging members surrounding saidelectrode, one of said members abutting the lower end of said first named insulating member, and the other abutting the upper end ofsaid secondnarned insulating member, and means engaging the outer surface of said casing to hold both the horizontally and obliquely disposed surfaces of said casing in clamping relation to said insulating'and lwedging members.

5. Afspark plug comprising a central. electrode,

an outer metallic casinghaving horizontally, ver- 5 tically and obliquely disposed inner surfaces, a tubular member of insulating materialY engaging said horizontally disposed surface at its upper end, a second insulating member surrounding said central electrode, a wedging memberabutting the upper surface of said second named' insulating member and'means for causing the obliquely disposed surface of said casing to exert a clamping'pressure, through the instrumentality of said Wedging member, upon both said insulating members.

6. A spark plug comprising a body structure provided with solid insulating materialcentrally apertured to different degrees, an electrode extending through the'portion of said insulating material which is-centrally apertu'red to the lesser degree, an ignition wirefprojected into theother apertured portion of said .insulating material lto establish connection with said electrode, azmetallic casing contacting said insulating material,

a metallic sheathV surrounding said ignition-wire,l

and means for electricallyfconnecting the metallic casingfwith the metallic sheath.

7. A sparkr plug comprising a center electrode, a shielded conductory engageable therewith, insulating including an insulating sleeve `fitting closely about the upper end of said electrode, a casingv built into the plug and constituting an integral part thereof and formed of ycomplementary upper and lower sections, oney of which fits closely about said insulating sleeve, means including interengaging screwthreads for holdr ing said sections in contact with each other and ifor electrically connecting said one of said sections withthe shielded conductor,

8. A spark plug comprising a casing formed -of complementary upper and lower sections, means including inter-engaging screw threads for holding said sectionsin contact with each other,

fan electrode passing centrally within said casing sections, a shielded conductor engageable with said electrode, means for holding the -shield of said conductor in electrical contact with one of said casing sections and solid insulating means completely filling the space between the upper end of said center electrode and one of said casing nected with said metallic cap.

l0. Ignitionapparatus comprising a metallic casing, an insulating lining engaging the inner surface of said casing, a central terminal centered within said casing, an ignition wire having a flexible electrical shield thereon, said shield being electrically bonded `with said casing and said ignition wire passing into said casing for establishing connection with said central ter- `minal, and bonding means comprising a coupling member threadedly engaging said casing and having an inwardly extending portion contacting said shieldfand a ring also contacting said shield and abutting said inwardly extending portion whereby attachment and tightening of the coupling. member causes said ring to press against said shield.

yl1. Ignition apparatus comprising a metallic casing, a central terminal centered within said casing, solid insulating means contacting said casing and lling the space between said casing and the outer end of said central terminal, an ignition wire having a iiexible electrical shield thereon, said ignition wire passing into said casing for establishing connection with said central terminal, means for electrically bonding said shield to said casing, said casing comprising a coupling member threadedly engaging said casing and having an inwardly extending portion, and a ring contacting said shield and abutting said inwardly extending portion whereby tightening of the coupling member causes said ring to press against `said shield.

l2. In a spark plug of the type having a metallic body adapted to be bonded to the electrical shield of a shielded ignition wire, the combination of a central electrode in said body, a'shielded ignition wire extending into said body and con- I' nected to said electrode, insulating means surrounding said electrode and wire and insulating vthe same from said body, wedgingmeans intermetallic cap and a stem having an outlet, a conductcr connecting t0 said stem at the outlet, a dielectric member seated against said cap and enclosing said outlet and a metallic coating enclosing said conductor and a metallic coating on said member electrically connected with said metallic cap, said coatings being in the form of a thin sheath.

14. In combination, a spark plug comprising a metallic shell and a stem having an outlet, a conductor connecting to said stem at the outlet, a dielectric member enclosing said outlet, and a metallic coating intimately encasing said member and grounded through said shell.

15. In combination, a spark plug comprising a metallic support and a stem having an outlet, a shielded conductor connecting to said stem at the outlet, a dielectric member enclosing said outlet, and a metallic sheath projecting from said support and contacting said member and grounding the shield on said conductor through said support.

16. In combination, a spark plug for aircraft engines including a stem having a terminal, metallic supporting means for said stem, a'dielectric member seated against said supporting means and closely surrounding said terminal, metallic enclosing means intimately contacting said member, a conductor having a terminal for connection to said first named terminal, said terminals providing a quickly detachable connection by telescopic movement of one of said terminals with respect to said member and its metallic enclosing means into engagement with the other of said terminals, and metallic enclosing means encasing said conductor and electrically connected with said means enclosing said member, both said enclosing means being grounded through said supporting means and providing a complete electrically conductive shield for said stem and said conductor.

17. In combination, a spark plug for aircraft engines including a stem having a terminal, metallic supporting means for said stem, a dielectric member closely surrounding said terminal, metallic enclosing means intimately contacting said member, a conductor having a terminal for connection to the said first named terminal, said terminals providing a readily attachable and detachable connection by movement of one of said terminals into and out of engagement with the other of said terminals, metallic enclosing means encasing said conductor, and means for detachably connecting said last named enclosing means to the free end of said first named enclosing means to provide an electrical connection therebetween, both said enclosing means being grounded through said supporting means and providing a complete electrically conductive shield for said stem and said conductor.

1B. In combination, a spark plug for aircraft engines including a stem having a terminal, a threaded shell for engagement with a'threaded aperture in the engine cylinder Wall, metallic means for supporting said stem threadedly mounted in said shell, solid dielectric means seated against said supporting means and enclosing said terminal, metallic enclosing means intimately contacting said dielectric means, said dielectric means substantially lling the space between said stem and its enclosing means, a conductor having'a terminal for connection to said first named terminal, metallic enclosing means encasing said conductor, and means for electrically connecting said last named enclosing 19. In combination, a spark plug for aircraft engines including a stem having a terminal, dielectric means closely embracing said stem, a threaded shell for engagement with a threaded aperture in the engine cylinder wall, metallic means for supporting said stern and dielectric means threadedly mounted in said shell, a dielectric member seated against said supporting means and overlapping the said dielectric means embracing said stem, metallic enclosing means intimately contacting said dielectric member, a conductor having a terminal for connection to said rst named terminal, metallic enclosing means encasing said conductor, and means for electri cally connecting said last named enclosing means to the end of said first named enclosing means. said enclosing means for said dielectric member providing with said metallic supporting means a complete electrically conductive sheath from said metallic means encasing said conductor to said threaded shell grounded in said cylinder wall and said dielectric means and member substantially filling the space between said sheath and said stem.

20. In a spark plug, a cylindrical metal spindle having a terminal end adapted to receive an ignition current, an outer metal sleeve around the terminal end portion of said spindle and extending a substantial distance beyond the terminal end thereof, an insulated ignition current con ductcr entering said sleeve and having an exposed terminal end establishing electrical connection to said spindle, a metallic casing for said conductor connected to the free end of said sleeve and forming therewith a shield for said conductor and spindle, and continuous insulation contacting said sleeve and substantially lling the space between said sleeve and the outer end of said spindle, said insulation extending a substantial distance beyond the terminal end of said spindle between the extended end of said sleeve and the insulation surrounding said conductor, whereby the outer sleeve is eiTectively insulated from the spindle and the exposed end of the conductor.

2l. In In combination, a spark plug for aircraft engines including a stem, metallic supporting means for said stem, dielectric means closely embracing said stem and having a tubular portion surrounding the outer end thereof, a metallic sleeve contacting the outer face of said dielectric means and forming an electrical connection with said supporting means, said dielectric means substantially filling the space between said stem and said sleeve, an insulated conductor provided with a terminal for connection to the end of said stem, a metallic sheath for said conductor, and means maintaining an electrical connection from said sheath to said sleeve, said tubular portion of said dielectric means providing a recess in which said terminal is connected to Asaid stem; and said sheath, said sleeve and said metallic supporting means being electrically connected to ground and providing a complet-e shield for said conductor, said stem and the connections therebetween.

22. In a shielded spark plug, the combination of an insulated spindle, a body in which said spindle is fixed, a metal barrel extending from the body above the spindle to form a socket and part ol the shielding of the plug, an insulated hightension conductor insertable into said socket to make electrical connection with said spindle, a metallic sheath about said conductor outside the spark plug, a metal connection through which the insulated conductor is passed and to which said sheath is connected, said connection having detachable engagement withsaid barrel, a tip piece fastened to the conductor wire, and an insulating sleeve about the portion of the insulated conductor withinthe socket, said sleeve being located between said tip piece and said-detach able connection.

23. A spark plug comprising, in combination, a central spindle having a head at its lower end, a body including a sleeve extending around the upper part of the spindle and above its upper end, an insulation of mica about the spindle extending from said head substantially to the upper end of the spindle, a second insulation of mica lining said sleeve, and extending from below the outer end of the first insulation to a point above the upper end of the spindle, and an insulation of mica disks held against the head of the spindle.

24. In combination, a spark plug for aircraft engines including a stem having a terminal, metallic supporting means for said stern, a dielectric member seated against said supporting means and closely surrounding said terminal, metallic enclosing means intimately contacting said member, a conductor having a terminal for connection to the said first named terminal said terminals providing a quickly detachable connection by telescopic movement of one of said terminals into engagement with the other of said terminals, metallic enclosing means encasing said conductor, and a coupling nut contacting said last named enclosing means and threadedly engaging the free'end of said first named enclosing means to provide an electrical connection therebetween, both said enclosing means being grounded through said supporting means and providing a complete electrically conductive shield for said stem and said conductor.

25. A shielded spark plug for a radio receiver equipped vehicle, comprising a metallic outer shell having an opening at the top thereof, an insulating body within said shell having a recess at the top portion thereof. an electrode extending through said-body and terminating in said recess, a metallic recessed apertured cap through which an insulated electrical conductor may extend and having means for attachment to said shell at the opening thereof, and an insulating bushing disposed belowlsaid cap and extending into the recess of the insulating body, said bushing snugly surrounding said conductor.

26. In combination, a spark-plug for internal combustion engines, comprising a metal jacket having therein an electrode spaced from the jacket by insulating material, said electrode and insulating material projecting from one end of the jacket, an insulated conductor electrically connected to said projected end of said electrode and having metallic shielding covering the insulation thereon, a dielectric member surrounding and closely fitting the said projecting end of the electrode insulating material for at least a substantial distance of its length and enclosing the connected end portions of said conductor and said electrode, and a relatively thin metallic shielding covering and in contact with theexterior surface of said dielectric member whereby a shielded spark-plug of reduced dimensions is produced. said shielding being electrically connected at cf ntiguous ends thereof and adapted to be grounded to the engine with which the spark-plug is used.

27. In combination, a spark-plug for internal combustion engines, comprising a metal jacket having therein an electrode spaced from the jacket by insulating material, said electrode and insulating material projecting from one end of the jacket, an insulated conductor electrically connected to said projecting end of said electrode and having metallic shielding covering the insulation thereon, a dielectric member surrounding and closely fitting the said projecting insulating material and enclosing the connected end portions of said conductor and s'aid electrode, and a metallic shielding encasing said dielectric member and in contact with the exterior surface thereof and electrically connected at one end with the shielding on the conductor and with said metal jacket at its other end.

28. In combination with a spark-plug including a plug terminal, an insulator anda metal shell of a hollow insulator fitting over the plug terminal and in surrounding contact with the sparkplug insulator, said hollow insulator having an aperture in its wall adapted to admit a hightension cable, means within said hollow insulator for electrically connecting the cable conductor to the plug terminal, and an electrically continuous metal sheathing extending over the outside of said hollow insulator lin close contact therewith and with the exposed surface of the cable, said sheathing beinggrounded.

29(1n combina-tion with a spark-plug including a plug terminal, an insulator and a metal shell, of a hollow insulator litting over the plug terminal and in surrounding contact with the sparkrlug insulator, said hollow insulator having an aperture in its Wall adapted to admit a hightension cable, means within said hollow insulator for electrically connecting the cable conductor to the plug terminal, an electrically continuous metal sheathing extending over the outside of said hollow insulator in close contact therewith and with the exposed surface of the cable, and common detachable means securing said hollow insulator and its sheathing to the plug and grounding said sheathing to said shell.

30. A shielded spark plug and electrical conductor cable for suppressing radio and other electrical disturbances comprising, a shielding for the plug and a shielding for the cable secured together near one end of said plug, the shielding for the plug forming a part of the grounded portion of the plug, the conductor of said cable extending within the plug shielding, the

.terminal of said conductor being electrically connected to the terminal of said plug, and insulating means within the plug shielding in contact therewith for enclosing the inner end of the cable at the cable terminal.

3l. A shielded spark plug and electrical conductor cable for suppressing radio and other electrical disturbances comprising, /a shielding for the plug and a shielding for the cable tsecured together near one end of said plug, the shielding for the plug being electrically connected to the grounded portion of the plug, the conductor of said cable extending within the plug shielding, the terminal of said cable conductor being connected to the terminal of said plug, insulation material disposed within said plug shielding and around said cable, said insulation being in intimate contact with said plug shielding Iserving to electrically separate said shielding and cable plug terminal connection and means within said plug shielding and between said cable and said insulation means to protect the cable.

- electrical disturbances comprising, a shielding for the plug and a shielding for the cable secured together near one end of said plug, the shielding for the plug being secured to the grounded portion of the plug, the insulation surrounding the conductor of said cable extending `within-the plug, and insulation means surrounding said cable including electrical insulating material in intimate contact with said plug shielding and electrically separating said vplug shielding and cable plug terminal connection, and a member disposed within said plug shielding and cooperating with said insulation means to protect the cable insulation.

33. In combination with an engine, a radio shielded spark plug comprising a metallic shell threaded to said engine, and a core having a stem provided with an outletelectrically connected with a conductor cable, a metallic shield inclosing said stem and grounded to said engine, a dielectric for insulating said electrical connection, said dielectric having intimate contact with said shield and having an aperture to receive a terminal portion of said conductor cable, and means to provide an enclosure for said terminal portion. y

34. A shielded spark plug and electrical conductor cable for suppressing radio and other electrical disturbances comprising, a shielding for the plug and a shielding for the cable secured together near one endof said plug, the shielding for the plug being electrically connected to the grounded portion ofthe plug. the conductor of said cable extending within the plug shielding, the terminal oi' said conductor being connected to the terminal oi said plug, insulation material disposed within said plug shielding and around said cable, said insulation serving to electrically separate said shielding and cable-plug terminal connection and having suriace contact with said shielding and a sleeve of insulation material surrounding the end of the conductor within the plug shielding and'separating said end from said electrical insulation.

35. In a spark plug, in which there is a body, a central spindle insulated from the body, and a metal barrel extending upward from the body above the upper end of the spindle `to provide a socket for the insertion of an insulated hightension conductor, a rolled mica sleeve lining said barrel and also in contact with said spindle, and means at the upper end of the barrel adapted to extend over the upper edge oi' said mica sleeve so as to contact with its layers and protect vover the upper `edge of said insulating lin the sleeve when the conductor is inserted and removed.

36. In a spark plug. in which there is a body, a central spindle insulated from the body, and a metal barrel extending upward from the body to provide a socket for the insertion of an insulated high-tension conductor, a mica sleeve lining said barrel, means at the base of the barrel having a `tapered bore, and unitary metallic means adapted to be wedged between said mica sleeve and said tapered bore, thereby creating suiicient pressure in a lateral`direction to insure retention of the4 central spindle against axial movement.

37. In a spark plug, inwhich there is a body, a central spindle insulated from the body, and a metal barrel extending` upward from the body above the upper `end of the spindle to provide a socket for the insertion of an insulated hightension conductor, insulating material defining the transverse limits of said socket and constituting a lining for said barrel, and means at the upper end oi the barrel adapted to extend so as to contact permanently with said un edge tothereby protect said lining when conductor is inserted and removed.

38. A shielded spark plug and electrical con ductor cable for suppressing radio and other electrical disturbances comprising, a shielding for the plug and a shielding for the cable cured together near one end ci said plug, the

shielding `for the plug being secured to the grounded portion of the plug, the insulation surrounding the conductor of said cable shielding extending within the plug, and ii'lsulation means surrounding said cable includingy electrical insulating material in intimate Contact with said plug shielding and electrically separating said plug shielding and cable plug terminal connection, and a heat conducting member cooperating `with said insulating material to 'provide a path of escape for some of the heat within said plug, said insulating material inclosing the plug terminal.

39. In a spark` plug assembly, the combination with a spark plug provided with a socket of insulating material and a spindle centered in` .said socket, of an electric lead adapted to be .intruded into the socket to make electric connection with the spindle, and :means cooperating with a portion of said insulating material insure maintenance oi firm Contact yw insulating material and the lateral sur said spindle.

LAWRENCE 

